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Al-Based Contacts on Ga-face and N-face n-GaN Wafer Grown by Using Hydride Vapor Phase Epitaxy
곽준섭,Cheolsoo Sone,Jaehee Cho 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.6
The effect of crystal polarity on the electrical properties of Al-based contacts to the Ga-face and the N-face n-GaN wafer has been investigated. The Al-based contacts prepared on the Ga-face n-GaN wafer exhibited linear I-V characteristics after annealing at 500 C for 90 min. On the contrary, the contacts on the N-face n-GaN wafer showed a nonlinear I-V curve. X-ray photoemission spectroscopy indicated that AlN could be produced at the interface between GaN and the contact metals after the annealing. High-resolution photoemission spectroscopy suggested that the differences in I-V characteristics of the Al-based contacts on the Ga-face and the N-face n-GaN could be explained by opposite piezoelectric fields at the GaN/AlN heterostructure resulting from different polarities of the GaN wafer.먉룮
Cho, Jaehee,Sone, Cheolsoo,Park, Yongjo,Yoon, Euijoon WILEY-VCH Verlag 2005 Physica status solidi. PSS. A, Applications and ma Vol.202 No.9
<P>The junction temperature rise of light emitting diodes due to self-heating effects during operation of the LED is measured using the electro-luminescence of the band-to-band recombination. This method is useful for the junction temperature monitoring of small geometry devices, indirectly. The junction temperature measured in InGaN/GaN multi-quantum well LEDs with 1 mm<SUP>2</SUP> device size rises to 180 °C when the input current is 380 mA. The relationship between the junction temperature and the LED efficiency is clarified with experimental results. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>
FDTD Simulation for Light Extraction in a GaN-Based LED
최원준,박규환,Cheolsoo Sone,Dongho Kim,전헌수,Yongjo Park 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.3
It is well known that light extraction from an LED can be enhanced by roughening the surface of the LED on a wavelength scale. However, the surface structure for optimal extraction and the underlying physical mechanism for increased emission are still largely unknown. In this work, we present both numerical and experimental studies on light extraction in GaN-based LEDs with square lattice photonic crystal patterns by using large-scale, three-dimensional FDTD (finite-difference time-domain) simulations, and we establish a reasonable simulation environment, including boundary conditions, and practical simulation specs, including source conditions. We show that these numerical results agree reasonably well with the experimental results. In particular, we explain the relationship between frequency and surface structure in light extraction. This allows us to suggest optimal practical structures for enhanced LEDs.
Reduction of efficiency droop in GaInN/GaN light-emitting diodes with thick AlGaN cladding layers
An Mao,조제희,E. Fred Schubert,Joong Kon Son,Cheolsoo Sone,하우진,Sunyong Hwang,김종규 대한금속·재료학회 2012 ELECTRONIC MATERIALS LETTERS Vol.8 No.1
GaInN/GaN multiple-quantum-well light-emitting diodes (LEDs) with 0.4 µm-thick AlGaN cladding layers and two quantum wells (QWs), designed for investigating the origin of efficiency droop, are demonstrated to have a lower efficiency droop than typical GaInN/GaN LEDs with 5 QWs. Considering the much less electron leakage over the active region, and the larger carrier density due to the smaller active volume of the LED with AlGaN cladding layers than those of the typical LED, it is suggested that the dominant mechanism responsible for the efficiency droop is electron leakage rather than the Auger recombination which scales with the cubic power of the carrier density.
Ma, Ming,Mont, Frank W,Yan, Xing,Cho, Jaehee,Schubert, E Fred,Kim, Gi Bum,Sone, Cheolsoo Optical Society of America 2011 Optics express Vol.19 No.5
<P>We investigate the effects of the refractive index of the encapsulant on the light-extraction efficiency (LEE) of light-emitting diodes (LEDs) for GaN LEDs (n ??? 2.5) and AlGaInP LEDs (n ??? 3.0). For non-absorbing rectangular parallelepiped LED chips, as the refractive index of the encapsulant increases, the LEE first increases quasi-linearly, then increases sub-linearly, and finally a saturation is reached. Furthermore, LEDs with a dual-layer graded-refractive-index (GRIN) encapsulant (n(encapsulant 1) = 1.57 and n(encapsulant 2) = 1.41) is fabricated through a two-step curing process. We demonstrate that such an LED further enhances the LEE by reducing Fresnel reflection loss at the encapsulant/air interface by 35% compared with an LED encapsulated with a single-layer encapsulant (n(encapsulant) = 1.57).</P>
Guan-Bo Lin,Dong-Yeong Kim,Qifeng Shan,Jaehee Cho,Schubert, E. Fred,Hyunwook Shim,Cheolsoo Sone,Jong Kyu Kim IEEE 2013 IEEE photonics journal Vol.5 No.4
<P>The dependence of the polarization-induced electric field in GaInN/GaN multiple-quantum-well light-emitting diodes (LEDs) on the GaN quantum barrier (QB) thickness is investigated. Electrostatic arguments and simulations predict that a thin QB thickness reduces the electric field in the quantum wells (QWs) and also improves the LED efficiency. We experimentally demonstrate that the QW electric field decreases with decreasing QB thickness. The lower electric field results in a better overlap of electron and hole wave functions and better carrier confinement in the QWs. A reduced efficiency droop and enhanced internal quantum efficiency is demonstrated for GaInN/GaN LEDs when the QB thickness is reduced from 24.5 to 9.1 nm.</P>